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/*
*
* Copyright (c) 2004
* John Maddock
*
* Use, modification and distribution are subject to the
* Boost Software License, Version 1.0. (See accompanying file
* LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
*
*/
/*
* LOCATION: see http://www.boost.org for most recent version.
* FILE object_cache.hpp
* VERSION see <boost/version.hpp>
* DESCRIPTION: Implements a generic object cache.
*/
#ifndef BOOST_REGEX_OBJECT_CACHE_HPP
#define BOOST_REGEX_OBJECT_CACHE_HPP
#include <map>
#include <list>
#include <stdexcept>
#include <string>
#include <boost/config.hpp>
#include <boost/shared_ptr.hpp>
#ifdef BOOST_HAS_THREADS
#include <boost/regex/pending/static_mutex.hpp>
#endif
namespace boost{
template <class Key, class Object>
class object_cache
{
public:
typedef std::pair< ::boost::shared_ptr<Object const>, Key const*> value_type;
typedef std::list<value_type> list_type;
typedef typename list_type::iterator list_iterator;
typedef std::map<Key, list_iterator> map_type;
typedef typename map_type::iterator map_iterator;
typedef typename list_type::size_type size_type;
static boost::shared_ptr<Object const> get(const Key& k, size_type max_cache_size);
private:
static boost::shared_ptr<Object const> do_get(const Key& k, size_type max_cache_size);
struct data
{
list_type cont;
map_type index;
};
// Needed by compilers not implementing the resolution to DR45. For reference,
// see http://www.open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#45.
friend struct data;
};
template <class Key, class Object>
boost::shared_ptr<Object const> object_cache<Key, Object>::get(const Key& k, size_type max_cache_size)
{
#ifdef BOOST_HAS_THREADS
static boost::static_mutex mut = BOOST_STATIC_MUTEX_INIT;
boost::static_mutex::scoped_lock l(mut);
if(l)
{
return do_get(k, max_cache_size);
}
//
// what do we do if the lock fails?
// for now just throw, but we should never really get here...
//
::boost::throw_exception(std::runtime_error("Error in thread safety code: could not acquire a lock"));
return boost::shared_ptr<Object>();
#else
return do_get(k, max_cache_size);
#endif
}
template <class Key, class Object>
boost::shared_ptr<Object const> object_cache<Key, Object>::do_get(const Key& k, size_type max_cache_size)
{
typedef typename object_cache<Key, Object>::data object_data;
typedef typename map_type::size_type map_size_type;
static object_data s_data;
//
// see if the object is already in the cache:
//
map_iterator mpos = s_data.index.find(k);
if(mpos != s_data.index.end())
{
//
// Eureka!
// We have a cached item, bump it up the list and return it:
//
if(--(s_data.cont.end()) != mpos->second)
{
// splice out the item we want to move:
list_type temp;
temp.splice(temp.end(), s_data.cont, mpos->second);
// and now place it at the end of the list:
s_data.cont.splice(s_data.cont.end(), temp, temp.begin());
BOOST_ASSERT(*(s_data.cont.back().second) == k);
// update index with new position:
mpos->second = --(s_data.cont.end());
BOOST_ASSERT(&(mpos->first) == mpos->second->second);
BOOST_ASSERT(&(mpos->first) == s_data.cont.back().second);
}
return s_data.cont.back().first;
}
//
// if we get here then the item is not in the cache,
// so create it:
//
boost::shared_ptr<Object const> result(new Object(k));
//
// Add it to the list, and index it:
//
s_data.cont.push_back(value_type(result, static_cast<Key const*>(0)));
s_data.index.insert(std::make_pair(k, --(s_data.cont.end())));
s_data.cont.back().second = &(s_data.index.find(k)->first);
map_size_type s = s_data.index.size();
BOOST_ASSERT(s_data.index[k]->first.get() == result.get());
BOOST_ASSERT(&(s_data.index.find(k)->first) == s_data.cont.back().second);
BOOST_ASSERT(s_data.index.find(k)->first == k);
if(s > max_cache_size)
{
//
// We have too many items in the list, so we need to start
// popping them off the back of the list, but only if they're
// being held uniquely by us:
//
list_iterator pos = s_data.cont.begin();
list_iterator last = s_data.cont.end();
while((pos != last) && (s > max_cache_size))
{
if(pos->first.unique())
{
list_iterator condemmed(pos);
++pos;
// now remove the items from our containers,
// then order has to be as follows:
BOOST_ASSERT(s_data.index.find(*(condemmed->second)) != s_data.index.end());
s_data.index.erase(*(condemmed->second));
s_data.cont.erase(condemmed);
--s;
}
else
--pos;
}
BOOST_ASSERT(s_data.index[k]->first.get() == result.get());
BOOST_ASSERT(&(s_data.index.find(k)->first) == s_data.cont.back().second);
BOOST_ASSERT(s_data.index.find(k)->first == k);
}
return result;
}
}
#endif
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